1. Field of the Invention
The present invention relates to a method and apparatus for adjusting a first and a second array relative to each other in a printing device having a carrying structure for mounting the first and second arrays. The first array has nozzles arranged in a first row substantially parallel to a first direction for forming first marks on a recording substrate. The second array has nozzles arranged in a second row substantially parallel to the first direction for forming second marks on the recording substrate. In an attainable relative position, the first and second arrays at least partially flank each other, thereby defining a degree of a longitudinal overlap along the first direction.
The present invention also relates to a computer program product residing on a computer readable medium comprising instructions for causing at least one process unit to perform the method of any the present invention.
2. Description of Background Art
In an ink jet printer known from the background art and having at least a first and a second printhead, a carriage whereon the printheads are mounted is generally moved over a recording substrate in a main scanning direction parallel to a y-axis for the purpose of recording a swath of an image. The first and second printheads have respectively first and second arrays of nozzles extending in a direction substantially parallel to the x-axis, which is the sub-scanning direction. The sub-scanning direction x is perpendicular to the main scanning direction y. An image swath consisting of a certain number of pixel lines, corresponding to the number of activated nozzles of the printheads is thus recorded during a pass of the carriage along the main scan direction. In a given relative position of the first and second arrays along the x-axis, the first and second arrays at least partially flank each other and are arranged for forming respectively first and second marks (also referred to as dots) on a substrate. Some pixel lines are thus constituted by first marks, corresponding to the nozzles of the first row, while other pixel lines are constituted by second marks, corresponding to the nozzles of the second row. Since the first and second rows at least partially flank each other, pixel lines constituted by first marks and pixel lines constituted by second marks both are formed in a same image swath onto the recording substrate during a single pass of the carriage. Generally, interlacing of such pixel lines is desired to obtain a high resolution of the recording image. In addition, the spacing between the lines should be as regular as possible. During one single pass of the carriage with two printheads, a printing resolution twice as high as the resolution of a single printhead may be achieved. Therefore, the relative position of a first and a second printhead along the x-axis has to be adjusted with a high degree of precision. Furthermore, a common error in the positioning of the pixel lines is caused by jet angles which deviate from the ideal jet angle. Such defects may be caused by impurities present in the nozzles. Such defects may lead, for graphical applications, to the appearance of white or light stripes in an image, known as “banding.”
A method for adjusting a first and a second array relative to each other in a printing device of the type set forth is known from U.S. Pat. No. 4,675,696. In this patent, a reference pattern is recorded, wherein the reference pattern comprises “recording elements” formed by each printhead for detecting the relative positional aberration of the printheads in the sub-scanning direction. The recorded reference pattern is read for providing an output indicative of the relative locations of the “recording elements.” This enables a detection unit to provide an output indicative of the intervals between the printheads in the sub-scanning direction. This is turn enables a control unit to control and adjust the relative position of the printheads in the sub-scanning direction.
However, the method of the background art is not suited for adjusting the relative position of the first and second printheads such that interlaced pixel lines are obtained with a recording resolution twice as high as the resolution of a single printhead. Furthermore, the method according to the background art is not able to solve the problem of “banding.”